1. Field of the Invention
The present invention relates to a packet synchronization switching method at a gateway device for interconnecting systems/networks with different protocols (communication procedures). The present invention particularly relates to synchronization of data processing timings and packet processing in a device at which a packet-based interface is specified for connections between blades mounted in the device: for example, ATCA (Advanced Telecom Computing Architecture), which is a hardware standard for computers for communications businesses, or the like.
2. Description of the Related Art
FIG. 8 is a conceptual diagram illustrating basic structure of a related art ATCA device conforming to ATCA specifications.
The ATCA device is constituted with a shelf manager 1 that performs internal device management control, a switch blade 2-1 with a switching (SW) function for an intra-device local area network (LAN) between blades that are mounted, blades 2-2 to 2-n with application functions, and a backplane 3 with a distribution function for interconnecting the blades 2-2 to 2-n with the shelf manager 1 and the switch blade 2-1.
A maximum of 16 blades may be mounted, from the switch blade 2-1 to blade 2-n. The shelf manager 1 and the blades 2-2 to 2-n with the application functions are connected to the switch blade 2-1 for performing packet communications through a device internal LAN 3a. The shelf manager 1 is connected with the switch blade 2-1 to blade 2-n by a management bus 3b that is for performing management control of the blades 2-2 to 2-n. The switch blade 2-1 to blade 2-n are connected with a clock bus 3c that is for providing common clock signals in the device.
The switch blade 2-1 to blade 2-n carry out data processing, using the common clock signals as necessary. Transmission and reception of data between the blades 2-2 to 2-n is implemented by packet-based data transmission/reception via switches of the device internal LAN in the switch blade 2-1.
In communications equipment up to now, TDM (time division multiplexing) traffic has often been necessary for data transmission and reception between devices and between blades. As described in PICMG SFP.0 System Fabric Plane Format (Mar. 24, 2005) and PICMG SFP.1 Internal TDM (Mar. 24, 2005), packetization of TDM signals is specified in accordance with the ATCA specifications, and the ATCA specifications have come to be applied over a wider range.
Methods have been proposed for solving problems that arise when the ATCA specifications are applied to various devices. For example, in Japanese Patent Application Laid-Open (JP-A) No. 2008-9520, in relation to data transfers between the blades 2-1 to 2-n, a method is proposed for suppressing effects arising from delays in inter-blade data transfers due to the use of the packet-based device internal LAN 3a. 
FIG. 9 is a schematic structural diagram illustrating an example of a related art gateway device.
In order to simplify description, the shelf manager 1, which performs device internal management control, and the backplane 3, with the distribution function for interconnecting between the blades 2-1 to 2-n, of FIG. 8 are omitted from FIG. 9.
A gateway device 4 in FIG. 9 is a device for connecting between, for example, an IP (Internet protocol) network N1 and an SDH (synchronous digital hierarchy) network N2. The IP network N1 is a computer network that is interconnected using IP technology. The SDH network N2 is a synchronous network that is established in accordance with SONET (Synchronous Optical NETwork), which is specified by the ANSI (American National Standards Institute).
The gateway device 4 is equipped with plural blades 5-1, 5-2, etc. which have redundant structures (that is, identical structures), such as an operational sound processing blade 5-1 and a backup sound processing blade 5-2 and the like, and with an SDH network interface blade 6, a control blade 7 and a switch blade 8.
Each of the operational sound processing blade 5-1 and the backup sound processing blade 5-2 is structured with: a PKG control section 5a, an I-TDM processing section 5b including a packet (PKT) processing section 5b-1, an I-TDM (internal TDM)/TDM conversion section 5b-2 and a buffer 5b-3; a sound processing section 5c including a main sound processor 5c-1, a PKT processing section 5c-2 and a PKG retention section 5c-3; a clock reception section 5d; and so forth. The SDH network interface blade 6 is structured with a PKG controller 6a, an SDH/I-TDM conversion section 6b, an SDH terminal section 6c, and so forth. The control blade 7 is structured with a clock management section 7a, a clock transmission section 7b, a device control section 7c, and so forth. The switch blade 8 is structured with a PKG control section 8a, network (NW) switches 8b, and so forth.
The sound processing blades 5-1 and 5-2 are redundantly structured. The operational sound processing blade 5-1 performs sound processing based on a common clock provided from the control blade 7, outputs packets to the IP network N1 that is connected via the network (NW) switches 8b, and outputs data through the network (NW) switches 8b to the SDH network N2 via the SDH network interface blade. The backup sound processing blade 5-2 is in a standby state, stopping output of packets, until system switching is executed by the network (NW) switches 8b. 